Metered dose inhalers are well known in medicine for treatment, or alleviation of the effects of respiratory complaints, for example asthma. Breath-actuated devices are also known, and have been the subject of many patent applications.
GB 1288971; GB 1297993; GB 1335378; GB 1383761; GB 1392193; GB 1413285; WO85/01880; GB 2204799; U.S. Pat. No. 4,803,978 and EP 0186280A describe inhalation-actuated dispensing devices for use with a pressurised aerosol dispensing container. The device includes a dispensing container and the container includes a valve capable of releasing a metered amount of the aerosol contents, when an internal spring operating the valve is compressed by a sufficient amount. The dispensing device often comprises a chamber having a mouthpiece, air inlets, actuating means for causing the actuation of the valve in the dispensing container, a latching means for releasably retaining said metering valve in a charged position, and an inhalation responsive means for releasing the latch, such that a metered amount of aerosol compound is discharged into the region of the mouthpiece. The overall objective is to give co-ordination of discharge of medicament from the aerosol container with inhalation of the patient, thus allowing a maximum dose of medicament to reach the bronchial passages of the lungs.
The latching means is often connected to a valve which moves from a latching position to a dispensing position in response to a partial vacuum developed upon inhalation.
EP-A-0045419 describes an inhalation device having biassing means which are alone of insufficient force to depress the container but which together are of sufficient force to do so.
EP-A-186280 describes a device which employs magnets to control the release of the aerosol container.
U.S. Pat. No. 3,605,738 describes devices in which the aerosol container communicates with the mouthpiece via a metering chamber. A metered quantity of the aerosol compound is discharged into the metering chamber and this is conveyed to the mouthpiece via an inhalation-actuated valve.
GB 1269554 describes a device wherein the aerosol container is moveable by a lever and cam system into a charged position held by a latch, a pressure differential acting to trip the latch and move the valve of the container to a discharge position.
U.S. Pat. No. 5,447,150, incorporated by reference herein, disclosed a metered dose inhaler, wherein the release of the medicament is actuated by the inhalation of the patient. That patent disclosed an inhalation-actuated device which is more simple and compact than the then-prior art dispensers. In one disclosed form, a closed negative pressure region is defined in part by a diaphragm molded from a single material. The diaphragm includes a relatively thick central disk, surrounded by a relatively thin flexure and peripheral ring. That construction is difficult to fabricate, in part due to the differing thickness regions.